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Optics Letters

Design-flexible entanglement of two distant quantum dots bridged by dark whispering gallery modes

Yanhui Zhao

Published Nov 2, 2020• 3 citations
Publisher

Abstract

We present a flexible design to realize the entanglement between two distant semiconductor quantum dots (QDs) embedded in separated photonic crystal nanobeam cavities. When bridged by a largely detuned microring cavity, photonic supermodes between two distant nanobeam cavities are formed via whispering gallery modes (WGMs). Due to the large detuning, WGMs in the microring exhibit almost no photonic excitation, showing the "dark WGMs." With the dyadic Green's functions of the nano-structure and the resolvent operators of the Hamiltonian, we numerically investigate the entanglement dynamics of two distant QDs. Furthermore, we prove that the entanglement can be tuned by adjusting the distances between the cavities. Such a scheme paves an efficient way for realizing a scalable quantum network in a solid-state system.

DOI
10.1364/ol.408938

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We present a flexible design to realize the entanglement between two distant semiconductor quantum dots (QDs) embedded in separated photonic crystal nanobeam cavities. When bridged by a largely detuned microring cavity, photonic supermodes between two distant nanobeam cavities are formed via whispering gallery modes (WGMs). Due to the large detuning, WGMs in the microring exhibit almost no photonic excitation, showing the "dark WGMs." With the dyadic Green's functions of the nano-structure and the resolvent operators of the Hamiltonian, we numerically investigate the entanglement dynamics of two distant QDs. Furthermore, we prove that the entanglement can be tuned by adjusting the distances between the cavities. Such a scheme paves an efficient way for realizing a scalable quantum network in a solid-state system.
Scalable architectures for quantum information technologies require one to selectively couple long-distance qubits while suppressing environmental noise and cross talk. In semiconductor materials, the coherent coupling of a single spin on a quantum dot to a cavity hosting fermionic modes offers a new solution to this technological challenge. Here, we demonstrate coherent coupling between two spatially separated quantum dots using an electronic cavity design that takes advantage of whispering-gallery modes in a two-dimensional electron gas. The cavity-mediated, long-distance coupling effectively minimizes undesirable direct cross talk between the dots and defines a scalable architecture for all-electronic semiconductor-based quantum information processing.
We investigate the entanglement generation between two nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a high-Q counterpropagating twin whispering-gallery modes (WGMs) of a microtoroidal resonator. For looking into the degree and dynamics of the entanglement, we calculate the concurrence using the microscopic master equation approach. The influences of the coupling strength between the WGMs (or the size of the two spherical NV centers), the distance between two NV centers, the frequency detuning between the NV center and microresonator, and the initial state of the system on the dynamics of concurrence are discussed in detail. It is found that the maximum entanglement between the two NV centers can be created by properly adjusting these controllable system parameters. Our results may provide further insight into future solid-state cavity quantum electrodynamics (CQED) system for quantum information engineering.
We theoretically investigate a cavity quantum electrodynamics system in which a high-QQQ whispering-gallery-mode (WGM) microresonator interacts with multiple diamond nanocrystals each containing a single nitrogen-vacancy (NV) center. With a tapered fiber waveguide coupling the WGMs, the transmission spectrum of the system exhibits a twofold-splitting phenomenon, where the first fold of splitting originates from the nanocrystals' Rayleigh scattering and the second fold stems from the NV center dipole coupling with the WGMs. The interacting system can serve as a platform to generate quantum entanglement between two NV centers embedded in distant diamond nanocrystals. Our further study reveals that the Rayleigh scattering of the nanocrystals plays a positive role in generating entanglement in some cases. The analytical results show that the relatively strong scattering leads to a larger concurrence for the fixed dipole-cavity detunings. This investigation may hold potential for solid-state quantum information processing applications.
The quantum coupling of spatially distant spins via optical photons using cavity quantum electrodynamic (cQED) methods has proved experimentally challenging due to the large spin-photon coupling strengths required. To achieve such coupling strengths using traditional cQED methods requires either individual spins and ultra-small cavities or an ensemble of identical spins coupled to larger cavities. In this work we describe a method to couple distant spins via the collective enhanced coupling to a large ensemble ∼ N, of degenerate optical Whispering Gallery Modes (WGM) in a spherical resonator where the spins are spatially located at the antipodes. The setup can be scaled-up to build 1D, 2D and 3D cQED lattices to enable quantum simulation or computing.
We propose a scheme to realize robust optical entanglement in cavity optomagnonics, where two optical whispering gallery modes (WGMs) couple to a magnon mode in a yttrium iron garnet (YIG) sphere. The beam-splitter-like and two-mode squeezing magnon-photon interactions can be realized simultaneously when the two optical WGMs are driven by external fields. Entanglement between the two optical modes is then generated via their coupling with magnons. By exploiting the destructive quantum interference between the bright modes of the interface, the effects of initial thermal occupations of magnons can be eliminated. Moreover, the excitation of the Bogoliubov dark mode is capable of protecting the optical entanglement from thermal heating effects. Therefore, the generated optical entanglement is robust against thermal noise and the requirement of cooling the magnon mode is relaxed. Our scheme may find applications in the study of magnon-based quantum information processing.
We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.